1BTRFSTUNE(8) BTRFS BTRFSTUNE(8)
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6 btrfstune - tune various filesystem parameters
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9 btrfstune [options] <device> [<device>...]
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12 btrfstune can be used to enable, disable, or set various filesystem pa‐
13 rameters. The filesystem must be unmounted.
14 The common usecase is to enable features that were not enabled at mkfs
16 time. Please make sure that you have kernel support for the features.
17 You can find a complete list of features and kernel version of their
18 introduction at
19 https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature . Also,
20 the manual page mkfs.btrfs(8) contains more details about the features.
21 Some of the features could be also enabled on a mounted filesystem by
23 other means. Please refer to the FILESYSTEM FEATURES in btrfs(5).
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26 -f Allow dangerous changes, e.g. clear the seeding flag or change
27 fsid. Make sure that you are aware of the dangers.
28 -m (since kernel: 5.0)
30 change fsid stored as 'metadata_uuid' to a randomly generated
32 UUID, see also '-U'
33 -M <UUID>
35 (since kernel: 5.0)
36 change fsid stored as metadata_uuid to a given UUID, see also -U
38 The metadata_uuid is stored only in the superblock and is a
40 backward incompatible change. The fsid in metadata blocks re‐
41 mains unchanged and is not overwritten, thus the whole operation
42 is significantly faster than -U.
43 The new metadata_uuid can be used for mount by UUID and is also
45 used to identify devices of a multi-device filesystem.
46 -n (since kernel: 3.14)
48 Enable no-holes feature (more efficient representation of file
50 holes), enabled by mkfs feature no-holes.
51 -r (since kernel: 3.7)
53 Enable extended inode refs (hardlink limit per file in a direc‐
55 tory is 65536), enabled by mkfs feature extref.
56 -S <0|1>
58 Enable seeding on a given device. Value 1 will enable seeding, 0
59 will disable it. A seeding filesystem is forced to be mounted
60 read-only. A new device can be added to the filesystem and will
61 capture all writes keeping the seeding device intact. See also
62 section SEEDING DEVICE in btrfs(5).
63 WARNING:
65 Clearing the seeding flag on a device may be dangerous. If a
66 previously-seeding device is changed, all filesystems that
67 used that device will become unmountable. Setting the seeding
68 flag back will not fix that.
69 A valid usecase is 'seeding device as a base image'. Clear
71 the seeding flag, update the filesystem and make it seeding
72 again, provided that it's OK to throw away all filesystems
73 built on top of the previous base.
74 -u Change fsid to a randomly generated UUID or continue previous
76 fsid change operation in case it was interrupted.
77 -U <UUID>
79 Change fsid to 'UUID' in all metadata blocks.
80 The UUID should be a 36 bytes string in printf(3) format
82 "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished
83 fsid change, it will continue only if the UUID matches the un‐
84 finished one or if you use the option -u.
85 All metadata blocks are rewritten, this may take some time, but
87 the final filesystem compatibility is unaffected, unlike -M.
88 WARNING:
90 Cancelling or interrupting a UUID change operation will make
91 the filesystem temporarily unmountable. To fix it, rerun
92 btrfstune -u and let it complete.
93 -x (since kernel: 3.10)
95 Enable skinny metadata extent refs (more efficient representa‐
97 tion of extents), enabled by mkfs feature skinny-metadata.
98 All newly created extents will use the new representation. To
100 completely switch the entire filesystem, run a full balance of
101 the metadata. Please refer to btrfs-balance(8).
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104 btrfstune returns 0 if no error happened, 1 otherwise.
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107 This deprecated tool exists for historical reasons but is still in use
108 today. Its functionality will be merged to the main tool, at which
109 time btrfstune will be declared obsolete and scheduled for removal.
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112 btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
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115 2022
1165.18 May 25, 2022 BTRFSTUNE(8)